A nuclear level sensing gauge for a vessel 10 comprises a vertical source well 12 and one more level sensing detectors 22 mounted to vertically spaced nozzles, where the sources 30 in the source well 12 are distributed sources which emit a radiation pattern illuminating a length of greater than one inch of the respective level sensing nozzle, so that thermal expansion or contraction of the vessel 10 does not significantly alter radiation illuminating each detector 22. In a second embodiment, a vessel 10 includes plural level sensing nozzles and plurality of level sensing wells 12′, each nozzle and level sensing well 12′ positioned adjacent to one another such that a source in the well illuminates a detector 22 on the nozzle. Because the respective level sensing wells 12′ and level sensing nozzles are closely adjacent to one another, thermal expansion or contraction of the vessel does not significantly alter the illumination of the detector 22.